Cronbach's Alpha
A measure used to assess the internal consistency or reliability of a set of scale or test items.
What is Cronbach's Alpha?
Cronbach's alpha is a coefficient (ranging from 0 to 1) that evaluates how closely related a set of items are as a group. It is considered a measure of scale reliability, determining whether all questions in a survey or questionnaire are measuring the same underlying construct.
Why Cronbach's Alpha Matters
When researchers use a Likert scale questionnaire to measure a latent variable (like 'customer satisfaction' or 'job stress'), they must prove that the multiple questions reliably measure the same concept. Cronbach's alpha provides this statistical proof.
How to Interpret
A commonly accepted rule of thumb is that an alpha of 0.70 or higher indicates acceptable reliability. However, values above 0.95 may indicate redundancy (questions are too similar).
Example
A survey uses 5 questions to measure 'Employee Motivation.' If Cronbach's alpha is 0.85, it indicates a high level of internal consistency, meaning the 5 questions reliably measure the same underlying motivation construct.
Common Mistakes
- Assuming a high alpha means the scale is unidimensional (measures only one concept); alpha measures consistency, not dimensionality (which requires Factor Analysis).
- Failing to remove reverse-coded items before calculating the alpha, resulting in an artificially low or negative score.